1) Technical Field
This disclosure relates generally to implantable tensile load-bearing grafts having synthetic components stitched through biological components.
2) Description of the Related Art
Reconstruction of a ruptured anterior cruciate ligament (ACL) is one of the most common procedures performed by sports medicine surgeons today. Few would dispute the importance of the ACL to knee stability and function. Anatomic intra-articular reconstruction is common for ACL patients or those with function disability due to acute or chronic ACL deficiency.
However, some in the field previously stated that the ACL did not need repair if the associated meniscal and capsular pathology was appropriately addressed. They failed to recognize the importance of the ACL as the primary restraint to anterior translation of the tibia and the prevalence of isolated ACL rupture.
Various techniques address the problem of ACL rupture. Primary repair and substituting the ACL with extra-articular reconstructions using local structures are known techniques but considered outdated by many. A common repair procedure passes grafts through a tibial tunnel and intra-articularly. The proximal end of the graft is then passed through the condyle notch on the femur and secured on the lateral aspect of the femur or through a tunnel in the femur. Some procedures include a double-bundle: implanting two grafts to attempt to mechanically replicate the force loading of the ACL.
Soft-tissue grafts and synthetic prosthetic replacements are used for ACL repair. Common tissue replacements include fascia lata grafts, hamstring grafts, and quadriceps or patellar tendon (also referred to as patellar ligament) grafts.
FIGS. 1a and 1b illustrate a variation of an ACL graft made from patellar tendon. The graft has a tendon length in the middle of the graft and bone plugs at each terminal end of the graft. The bone can be integral with the tendon, having been the natural bone at the ends of the tendon before excising the graft from the host location, or can be attached to the tendon after the tendon is removed from the host location. The graft is shown having a generally rectangular cross-section, but circular cross-sectional (i.e., cylindrical) grafts are also used.
Synthetic ACL replacements include structures made from polyethylene, such as the Polyflex, porous PTFE (Teflon) grafts, such as the Proplast, and grafts using carbon fiber, Gore-Tex, Dacron, and polypropylene. The polypropylene graft known as the Ligament Augmentation Device (LAD) was the only one to gain widespread use. These synthetics often failed as they tended to stretch or fragment over time.
Biological graft strength varies with time after implant. Natural stressing of the graft is beneficial for long-term strengthening of the graft, but the failure stress of biological grafts decreases after implantation and before the strength of the graft increases. Accordingly, failure of biological grafts may occur during rigorous post-replacement physical therapy intended to strengthen the graft. On the other hand, synthetic grafts start strong after implantation, but are known to sometimes fail due to long-term issues such as stretching or fragmentation.
Accordingly, it is desired to provide an ACL graft that has the long-term strength and biocompatibility of a biological graft with the short-term strength of a synthetic graft.